This invention relates generally to a distributing chute for a furnace. More particularly, this invention relates to a distributing chute which is particularly well suited suited for use in a bell-less charging system of a blast furnace.
A bell-less charging system for a blast furnace is, for example, known from U.S. Pat. No. 3,880,302, all of the contents of which are incorporated herein by reference. It comprises a distributing chute which is mounted in the top of the blast furnace in a rotatable, pivotable manner. The underside of the distributing chute is subjected to the full heat radiation from the surface of the charge in the blast furnace.
Whereas it was possible until recently to do without a means of heat insulation on the underside of the distributing chute, this is no longer the case where contemporary blast furnace operating practice is concerned. For example, due to the injection of increasingly large quantities of pulverized coal into the blast furnace, the temperature at the surface of the charge may exceed 1000.degree. C. The underside of the chute is thus subjected to more and more intense heat radiation. Above a certain temperature, however, the high-temperature resistant steels of the chute body lose their heat-resistant quality and corrosion appears.
Various heat insulating devices for the underside of the distributing chute have been proposed to correct this problem. A double-walled distributing chute which is cooled by means of an inert gas is known from GB-A-1,487,527, all of the contents of which are incorprated herein by reference. However, the effectiveness of this cooling is ensured only if very high gas throughputs are employed. However, feeding of large gas throughputs into a rotatable, pivotable chute is problematic and difficult to achieve.
An improved means of heat insulation for the underside of the distributing chute is known from U.S. Pat. No. 5,252,063, all of the conents of which are incorporated herein by reference. The improved heat insulation is mainly achieved by means of an improved device for feeding the cooling medium into the rotatable, pivotable distributing chute. This proposed feeding device enables either a higher gas throughput through the chute or, preferably, cooling of the chute with cooling water in a closed cooling circuit. For the cooling water, one or two U-shaped cooling ducts are longitudinally mounted on the underside of the distributing chute and connected to a cooling water distribution system through the suspension shafts of the distributing chute. In DE-4216166 it is furthermore proposed that the cooling ducts be provided with cooling fins or gills in order to achieve more uniform cooling of the underside and/or that the cooling ducts be embedded in a refractory material (e.g. a heat-insulating concrete).
Practical experience has shown in the meantime that embedding of the cooling ducts in a refractory material is emphatically recommended in order to protect the cooling ducts themselves as well as the underside of the distributing chute more effectively from the heat radiation (and from the generally hostile and severe conditions which prevail above the surface of the charge). Without the additional heat insulation of the refractory material, the throughput of the cooling medium would have to be increased substantially and the cooling ducts would have to be laid very close together on the chute body, both of which are not easily feasible.
Unfortunately it has also been discovered in the meantime that the refractory material in which the cooling ducts are embedded develops cracks relatively quickly in the furnace and crumbles away from or drops off the underside of the chute in relatively large, slab-like pieces.